Motor vehicle transmissions commonly employ an add-on "overdrive" gearbox to provide an additional gear ratio. Some applications use this overdrive gearbox to "compound" the ratio of additional gears. Typically, such "compounders" include a planetary gearset and one or more clutches that can be selectively actuated to establish one of a direct-drive mode and an overdrive mode. As is known, the direct drive mode provides a one-to-one gear ratio which enables the compounder to, in effect, be by-passed by the transmission. On the other hand, the overdrive mode provides a gear ratio other than one-to-one which provides the transmission with a simple and relatively inexpensive additional drive gear.
In many compounders, the input shaft and the output shaft are coaxially disposed in a housing. A direct drive device is employed to directly interconnect the input shaft to the output shaft so as to establish the direct drive mode. Over-running (i.e., one-way) clutches are typically used for the direct drive device. An overdrive device is similarly employed to interconnect the input shaft to the output shaft so as to establish the overdrive mode. In many instances, the overdrive device includes a planetary gearset and a selectively engageable mode clutch. In particular, the overdrive mode is commonly achieved by actuating the mode clutch to fix a sun gear of the planetary gearset to the housing, whereby an output member of the planetary gearset is driven at an increased speed ratio. Some examples of conventional compounders are disclosed in U.S. Pat. Nos. 4,484,494; 4,567,788; 4,649,771; 4,798,103 and 4,976,671. While such compounders have proven to work satisfactorily for their intended purpose, a need exists to minimize packaging and complexity while concomitantly advancing the state of the art.